1. Field of the Invention
The invention is directed to an improved high-pressure fuel pump for an internal combustion engine, the pump having a piston oscillating in a cylinder, in which the cylinder and the piston define a pumping chamber, and the pumping chamber communicates on the intake side with a low-pressure fuel line and on the compression side with a high-pressure fuel line, and having a quantity control valve located between the low-pressure line and the pumping chamber.
2. Description of the Prior Art
High-pressure fuel pumps of the type with which this invention is concerned are known, for instance from German Patent Disclosure DE 198 34 120 A1, DE 100 52 629 A1, or DE 102 00 987 A1. In all these high-pressure fuel pumps, the pumping quantity of the high-pressure pump is controlled by limiting the pumping of the fuel from the pumping chamber into the high-pressure fuel line during the pumping stroke. In the preceding intake stroke, when the piston moves from top dead center TDC to bottom dead center BDC, the pumping chamber becomes completely filled with fuel. As a consequence, in partial-load operation of the high-pressure pump, the fuel not pumped into the high-pressure fuel line is pushed back into the low-pressure fuel line via the quantity control valve. This aspiration of fuel from the low-pressure fuel line into the pumping chamber and the ensuing at least partial pushing back of this fuel into the low-pressure fuel line impairs the partial-load efficiency of these high-pressure fuel pumps and leads to unwanted warming of the fuel. The diversion of the excess fuel quantity from the pumping chamber furthermore causes major pressure pulsations in the low-pressure fuel line. These pressure pulsations must be absorbed or reduced by a damping device. For safety reasons, because of these pressure pulsations, the entire low-pressure region of the fuel injection system must also be able to withstand very high pressures. This increases the costs for a fuel injection system considerably.
In a method for controlling the pumping quantity of a high-pressure fuel pump for an internal combustion engine, having a piston oscillating in a cylinder, in which the cylinder and the piston define a pumping chamber, and the pumping chamber communicates on the intake side with a low-pressure fuel line and on the compression side with a high-pressure fuel line, and having a quantity control valve located between the low-pressure fuel line and the pumping chamber, it is provided according to the invention that the hydraulic communication between the pumping chamber and the low-pressure fuel line is opened, while the piston is moving from top dead center in the direction of bottom dead center. Next, the hydraulic communication between the pumping chamber and the low-pressure fuel line is interrupted, as soon as the fuel quantity to be pumped has been aspirated into the pumping chamber. In a further step, the aspirated fuel quantity is pumped into the high-pressure fuel line while the piston is moving from bottom dead center in the direction of top dead center.